It is well known that the neurotransmitters, dopamine (DA), norepinephrine (NE), and serotonin (5-HT), regulate a number of biological processes and that decreased levels of DA, NE, and 5-HT are associated with a number of neurological disorders and their physical manifestations. Significant effort has been expended on devising methods for adjusting the levels of these neurotransmitters in order to produce a desired pharmacological effect. Preventing the reuptake of these neurotransmitters in any combination of one, two, or all three of them is likely to be effective in treating these disorders. Targeting the dopamine transporter (DAT), norepinephrine transporter (NET), and the serotonin transporter (SERT) proteins has proven to be an effective way of increasing the levels of the respective monoamines.
Methylphenidate, which is currently used for the treatment of attention deficit hyperactivity disorder (ADHD), is known to be selective for inhibition of the DAT. U.S. Pat. No. 5,444,070 discloses selective inhibitors of dopamine reuptake as treatments for Parkinson's disease and drug addiction or abuse including cocaine and amphetamines.
Selective norepinephrine reuptake inhibitors (NARI) have also been disclosed. For example, U.S. Pat. No. 6,352,986 describes methods of treating ADHD, addictive disorders, and psychoactive substance use disorders with Reboxetine. In addition, Atomoxetine (Strattera®) is currently marketed as a selective NET reuptake inhibitor for ADHD.
The use of selective serotonin reuptake inhibitors (SSRI) has also been shown to be effective in treating depressive disorders. Sertraline, Citalopram, and Paroxetine are well-known examples of SSRIs used to treat disorders such as depression, obsessive compulsive disorder, and panic attacks. There are several known difficulties with the SSRI class of therapeutics, including the slow onset of action, unwanted side effects, and the existence of a significant subset of the population that is not responsive to SSRI therapy.
Selective inhibitors of DAT, NET, and SERT reuptake may also be co-administered with each other or with other drugs. U.S. Pat. No. 5,532,244 discloses the use of serotonin reuptake inhibitors in combination with a serotonin 1A antagonist for the treatment of obsessive-compulsive disorder, depression, and obesity. The use of a serotonin or norepinephrine reuptake inhibitor in combination with a neurokinin-1 receptor antagonist has been disclosed in U.S. Pat. No. 6,121,261 for the treatment of ADHD. U.S. Pat. No. 4,843,071 discloses the use of a norepinephrine reuptake inhibitor in combination with a norepinephrine precursor in the treatment of obesity, drug abuse, or narcolepsy. U.S. Pat. No. 6,596,741 discloses the use of a NE, DA, or 5-HT inhibitor with either a neurokinin-1 receptor antagonist or a serotonin-1A antagonist for the treatment of a wide variety of conditions.
Also advantageous is the use of compounds that inhibit one or more of the neurotransmitters at the same time. The antidepressant qualities of the dual NET and SERT reuptake inhibitor duloxetine is disclosed in European Patent No. 273658. Venlafaxine is disclosed in U.S. Pat. No. 4,535,186 as a reuptake inhibitor of both NE and 5-HT for the treatment of depressive disorders. U.S. Pat. No. 6,635,675 discloses the use of the dual NE and 5-HT reuptake inhibitor milnacipran for the treatment of chronic fatigue syndrome and fibromyalgia syndrome. In addition, dual NE and 5-HT reuptake inhibitors are disclosed in U.S. Pat. No. 6,136,083 for the treatment of depression. It is also recognized that compounds which inhibit the reuptake of NE, DA, and 5-HT in varying ratios not specifically mentioned here would also be advantageous.
Treating illnesses by inhibiting the reuptake of all three of the monoamines, either through combination therapy or “triple inhibitors,” may have clinical benefit as well. PCT International Publication Nos. WO 03/101453 and WO 97/30997 disclose a class of compounds which are active against all three monoamine transporters. The rationale for the inclusion of a dopamine-enhancing component in antidepressant therapy includes observed deficits in dopaminergic function, the success of combination therapy with dopamine agonists and traditional antidepressants, and an increased sensitivity in dopamine receptors due to chronic antidepressant administration (Skolnick et al., Life Sciences 73:3175-3179 (2003)). As such, inhibitory activity against DA reuptake, in addition to NE and 5-HT reuptake, is expected to provide a more rapid onset of antidepressant effect, compared to other mixed inhibitors which are selective for NET and SERT over DAT. In addition, PCT International Publication No. WO 03/049736 discloses a series of 4-substituted piperidines, each of which displays similar activity against DA, NE and 5-HT transporters. Bicyclo[2.2.1]heptanes (Axford et al., Bioorg Med Chem Lett 13:3277-3280 (2003)) and azabicyclo[3.1.0]hexanes (Skolnick et al., Eur J Pharm, 461:99-104 (2003)) are also described as triple inhibitors of the three monoamine transporters.
U.S. Pat. No. 3,947,456 discloses tetrahydroisoquinolines which are said to have utility as antidepressants. U.S. Pat. No. 3,666,763 describes the use of phenyl tetrahydroisoquinoline derivatives as antidepressants and antihypotensives. Canadian Patent Application No. 2,015,114 discloses the use of phenyl tetrahydroisoquinoline derivatives as antidepressants; the compounds described therein are apparently nonselective as to norepinephrine, serotonin, and dopamine uptake. United Kingdom Patent Application No. 2,271,566 discloses the use of phenyl tetrahydroisoquinoline derivatives as anti-HIV agents. PCT International Publication No. WO 98/40358 discloses the use of phenyl tetrahydroisoquinoline derivatives to be useful in the treatment of disorders of glucose metabolic pathways. PCT International Publication No. WO 97/36876 discloses the use of phenyl tetrahydroisoquinoline derivatives as anticancer agents. PCT International Publication No. WO 97/23458 also describes 4-phenyl-substituted tetrahydroisoquinolines as NMDA receptor ligands useful for conditions associated with neuronal loss. Phenyl-substituted tetrahydroisoquinolines are also described in Mondeshka et al., II Farmaco 49:475-481 (1994).
U.S. Pat. No. 6,579,885 discloses the use of 7-aryl-substituted tetrahydroisoquinolines as being useful for the treatment of disorders involving decreased availability of serotonin, norepinephrine, or dopamine. Tupper et al., J Heterocyclic Chem 33:1123-1129 (1996) describes the synthesis of tetrahydroisoquinolines substituted with a 2- or 3-thienyl group in the 4 position as possible dopamine D1 and D2 antagonists. Prat et al., J Heterocyclic Chem 37:767-771 (2000) describes the synthesis of N-methyl-4-pyridyl-1,2,3,4-tetrahydroisoquinolines, as well as the 2-pyridyl and 3-pyridyl analogs, which were designed as potential serotonin analogs, but no activity was reported. Chandrasekhar et al., Tetrahedron Lett 43:1885-1888 (2002) described the synthesis of trans-4-benzo[1,3]dioxol-5-yl-2-benzyl-3-methyl-1,2,3,4-tetrahydroisoquinoline; however, neither usage nor activity was reported. Lopez et al., Tetrahedron 50:9097-9106 (1994) described the synthesis of 2-(1,2,3,4-tetrahydroisoquinolin-4-yl)-quinolin-3-ol; however, neither usage nor activity was reported. Uno et al., J Heterocyclic Chem 38:341-346 (1991) described the synthesis of 1-ethyl-1′-pentafluoroethyl-1,2,3,4-tetrahydro-[4,4′]bis(isoquinoline); however, neither usage nor activity was reported.
Nomifensine®, which is a 4-phenyl-substituted tetrahydroisoquinoline derivative, is known to inhibit the neuronal uptake of dopamine and other catecholamines and has shown clinical efficacy for ADHD. However, long term administration of Nomifensine® resulted in fatal immune hemolytic anemia in a very small number of patients causing the manufacturer to discontinue this drug from the market. Thus, there continues to remain a need to develop novel compounds which treat ADHD but do not have the serious side effects associated with Nomifensine® or the currently prescribed psychostimulants.
The present invention is directed to achieving these objectives.